A complete quantum description of the 3(1)D state of helium, that is the am
plitudes and relative phases for the m = 0, +/-2 magnetic sublevels are rep
orted. All state multipoles [T(2)(kq)] (k = 0-4, k greater than or equal to
q greater than or equal to -k) that describe the population and the anisot
ropy of the excited He(31D) state are presented. The data were determined f
or 60eV incident electrons and 40 degrees electron scattering angle.
The experimental procedure was to measure the triple-coincidence, polarisat
ion correlations of the sequential cascading photons (667.8 nm 3(1)D --> 2(
1)P and 58.4 nm 2(1)P --> 1(1)S transitions) and the scattered n = 3 energy
loss electrons. Simultaneous measurements of the three two-particle coinci
dence pairs determined accurate magnitudes of the scattering amplitudes and
phases as well as enabling consistency checks with earlier data. The tripl
e coincidence data determined the sign of the relative m = +/-2 phases. The
results are presented in a simplifying diagrammatic form. As yet there are
no other complete experimental determinations of the 3(1)D state.
The measurements are in agreement, within the experimental uncertainty, wit
h the Convergent Close Coupling (CCC) calculations.
Previous data for helium at 40eV incident elections are discussed in the co
ntext of the present triple-coincidence results. The desirability of a rece
ntly introduced parameter notation for the helium 3(1,3)D states is questio
ned with respect to physical insight.